Without limiting the scope of the present invention, its background will be described with reference to perforating a hydrocarbon bearing subterranean formation with a shaped-charge perforating apparatus.
Two primary methods are extensively used to perform tubing-conveyed perforation (TCP) operations in the oil and gas recovery industry. A typical TCP assembly comprises an inner metallic tubular on which are mounted a plurality of shaped-charge explosives, positioned within an outer metallic tubular which acts as a housing, protective covering, fluid isolation, and tension and radial load bearing structure. The assembly includes detonation cords, etc., as are known in the art. The shaped charges, when fired, perforate the outer tubular, the casing (if present), and the formation. The outer and inner tubulars are often severely damaged, fragmented and misshapen during the process. The outer tubular, now perforated, often has projections extending at the circumferences of the perforations.
In one of the primary methods currently in use, any remaining portion of the TCP assembly, after firing, is pulled out of the casing and can be reloaded with charges and reused, if intact. However, this method has several disadvantages since in many drilling situations the inner tubular on which the shaped charges are mounted is damaged to such a degree that it cannot be removed from the hole without destroying the well.
The other method used in the industry is to utilize expendable TCP perforators to fire the charges. Following firing, the expendable perforating system is dropped to the bottom of the drilled hole that extends below the targeted formation, that is, into the rathole. However, drilling the rathole portion of the well requires additional drilling to depths as much as 2,000 feet beyond the target area so that the expended perforator can be accommodated. This extra drilling results in considerable additional time and drilling costs. In addition, the conventional metal tubing used for the TCP assembly generally fragments into large pieces of debris upon firing of the charges. These large pieces of metal debris often cause problems in fluid extraction, such as jamming of equipment, preventing tube removal, inhibiting fluid flow, contaminating the fluid, or clogging pumps or tubing used to extract the fluid.
Thus an expendable TCP assembly is needed which reduces these problems. The purpose of this invention is to develop a tubing conveyed perforator that does not require substantial additional rathole drilling and reduces the potential to clog oil extraction equipment with debris.